Pneumatically driven fastener driving tools are well known to those skilled in the art. One excellent example is described by A. Langas in U.S. Pat. No. 3,106,135 which is assigned to the assignee of the present invention. Another example is U.S. Pat. No. 3,815,475 by Howard and Wilson (also assigned to the assignee of the present invention). These tools have been well received by the industry and perform quite satisfactory. However, they have one basic shortcoming. Pneumatic tools must be provided with a continuous source of pressurized air or gas of a high order of magnitude to drive for example a 31/2 inch long nail. This is usually accomplished by a flexible hose joining the tool to a tank filled with pressurized gas or to an air compressor.
Such tools when used in a shop or a relatively restricted area present little inconvenience or burden on the user of the tool. However, when the tools are used "in the field," on construction sites and in remote areas, tools requiring an auxiliary power source become a burden and an inconvenience in addition to the large initial expense required for the investment of such equipment.
Fastener applying tools can be made portable by providing a self-contained source of power. However, if the energy required to operate the tool is high or if the tool must be operated rapidly or for a relatively long period of time, the power source used to operate the tool becomes limiting. None of the available portable tools that can drive large fasteners are capable of high speed operation for an extended period at an economically acceptable rate. Electric batteries, as such, are relatively bulky, high in weight, and do not provide a uniform source of power over a long period of time. A chemical source of power in the form of explosive pellets or shells can be used. However, the operating cost per unit fastener is quite high. In addition, those tools cannot be operated for a relatively long period of time without having the supply of shells or blanks refilled. The only form of self-contained power that would meet the power, speed and portability requirements is the efficient utilization of the power produced by the combustion of a fuel and air mixture within a confined space. U.S. Pat. No. 3,012,549 to Bard et al. and U.S. Pat. No. 4,200,213 to Liesse are examples of portable tools using internal combustion principles.
An examination of these earlier patents indicates a number of shortcomings which, if eliminated, would lead to greater acceptance by the industry. For the most part they have been relatively complicated, large, heavy machines which are awkward to use or manipulate. Some have required a separate tank to provide fuel for combustion. Still others employ timing mechanisms and pressure regulators which can easily come out of adjustment or be damaged during high volume, rapid rate work applications. Some of these earlier tools have required the user to manipulate more than one control lever or switch to cycle the tool. Moreover, the initial cost of the tool has been far in excess of a modern pneumatically powered fastener applying tool. In other words, an efficient, easy to operate, rugged, lightweight, low cost, truly portable fastener applying tool powered by the pressurized gas produced during the internal combustion of a fuel and air mixture is not currently available.